1. Field of the Invention
The present invention relates to a planar illumination apparatus.
2. Description of the Related Art
A planar illumination apparatus is used as a backlight of a liquid crystal display panel on a liquid crystal display apparatus. A sidelight-type planar illumination apparatus combining a light source as a light emitting element such as an LED with a light guide plate is widely used in a compact mobile information device such as a mobile phone (e.g. Japanese Patent Application Laid-open No. 2004-354727).
Such a planar illumination apparatus includes a frame-like light shielding member that defines an effective area for light emission. In order to realize miniaturization and design enhancement in the planar illumination apparatus, there is a demand for a narrower frame, that is, a demand for the light shielding member with a narrower width. For example, Japanese Patent Application Laid-open No. 2013-171723 discloses a planar illumination apparatus that realizes a narrower frame on two sides orthogonal to a light entrance side (light source placement side) of the light guide plate. This planar illumination apparatus has a structure in which a wiring substrate extends to cover a light entrance-side main surface of the light guide plate and an end portion of an optical sheet runs on the wiring substrate.
In recent years, the demand for a narrower frame is increasing not only on the two sides orthogonal to the light entrance side of the light guide plate but also on the light entrance side. The present inventors discovered, however, when the narrower frame on the light entrance side is implemented on the planar illumination apparatus having a structure in which the end portion of the optical sheet runs on the wiring substrate of the light source, as the planar illumination apparatus disclosed in Japanese Patent Application Laid-open No. 2013-171723, it would lead to a problem that luminance distribution of the outgoing light becomes unstable on a light emitting region on the light entrance side. The state in which the luminance distribution of the outgoing light is unstable implies the occurrence of uneven. luminance distribution of the outgoing light in a light emitting region on the light entrance side on a certain planar illumination apparatus and the occurrence of different luminance distribution of the outgoing light between different planar illumination apparatuses.
The present invention is made in view of the above description and is intended to provide a planar illumination apparatus that has realized a narrower frame and suppression of instability of luminance distribution of the outgoing light.